Electrolytic softening of water

ABSTRACT

A method of deionizing water having a dissolved solids content consisting largely of relatively insoluble calcium and magnesium salts by passing through the water a unidirectional electric current of sufficient voltage between electrodes immersed in the water to effect ionization thereof and recovering water substantially deionized and of a lesser degree of hardness. The electrolytic system includes a horizontally disposed container, preferably of dielectric structural material, for the feed water, horizontally spaced electrodes in the container between which the feed water is introduced and controlled means for removing substantially deionized water laterally of the electrodes and other controlled means for removing settled solids from below the space between the electrodes. The anode electrode is inert toward electrolytic action, while the cathode electrode need not be inert since under the conditions of operation it is not substantially corroded.

United States Patent Thompson [451 Mar. 28, 1972 [54] ELECTROLYTICSOFTENING OF WATER [21] Appl. No.: 766,050

[52] US. Cl. ..204/152, 204/149, 204/240,

204/275, 204/276 [51] Int. Cl. ..C22d l/02 [58] Field of Search ..204/149-1 52 [56] References Cited UNITED STATES PATENTS 1,746,964 2/1930Polatsik ..204/l49 1,901,652 3/1933 Kean ....204/l5l 2,640,026 5/1953Whittington..... ....204/l49 3,006,826 10/1961 Roller ....204/l493,441,488 4/ 1969 Onstott "204/ 149 Primary Examiner-T. TungAttorney-Hill, Sherman, Meroni, Gross & Simpson [5 ABSTRACT A method ofdeionizing water having a dissolved solids content consisting largely ofrelatively insoluble calcium and magnesium salts by passing through thewater a unidirectional electric current of sufficient voltage betweenelectrodes immersed in the water to effect ionization thereof andrecovering water substantially deionized and of a lesser degree ofhardness. The electrolytic system includes a horizontally disposedcontainer, preferably of dielectric structural material, for the feedwater, horizontally spaced electrodes in the container between which thefeed water is introduced and controlled means for removing substantiallydeionized water laterally of the electrodes and other controlled meansfor removing settled solids from below the space between the electrodes.The anode electrode is inert toward electrolytic action, while thecathode electrode need not be inert since under the conditions ofoperation it is not substantially corroded.

4 Claims, 4 Drawing Figures PATENTED MR 2 8 I972 llll l. Ill-II I'llELECTROLYTIC SOFTENING OF WATER SUMMARY OF THE INVENTION The inventionrelates to a method for the deionization and softening of natural waterscontaining a dissolved solids content consisting largely of relativelyinsoluble calcium and somewhat more soluble magnesium salts, and onlynegligible quantities of non-hardness-forming salts, such as sodiumchloride, insufficient to render the water appreciably conductive ofelectricity. The electrolytic deionization of the water is carried outin a system that includes a horizontally disposed container for thewater, a pair of spaced electrodes adapted to be immersed in the waterwithin the container, and controlled outlets disposed laterally of theelectrodes for the withdrawal of deionized water, together, optionally,with a controlled outlet below the space between the electrodes for theintermittent removal of water and any concentration therein of settledsolids. The anode is formed in an inert but electrically conductivematerial such as platinum or other inert heavy metal or alloy, carbon,graphite, or the like; and the cathode can be formed of any suitableconductive material, such as ferrous metal, stainless steel, or thelike, since it is not subjected in operation to appreciable corrosion.

A unidirectional current, capable of imposing a voltage differential ofbetween a minimum of about 4 to 5, and preferably of about 10 to lvolts, and a maximum of not over about 100 volts, and preferably notover 50 volts, is established between the electrodes. A current having avoltage between these limits that is sufficient to effect a flow ofelectrical current between the electrodes of between about 1 and 20, andpreferably 1 to milliamperes per square centimeter (ma/sq. cm.) iseffective to cause a deionization of the water, especially at thecathode, whereby a substantially deionized effluent can be withdrawnlaterally thereof. The system can be operated either continuously orbatch-wise. If continuous, the flow of feed water through the system iscontrolled as to rate of volume flow so as to effect the desired degreeof deionization and/or softening of the water, the degree beingdependent upon the purposes for which the deionized-water is to be used.

DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view ofapparatus suitable for carrying out the electrolytic system of myinvention;

FIG. 2 is a horizontal sectional view taken substantially along the lineIIII of FIG. 1;

FIG. 3 is a sectional view taken along the line IIIIII of FIG. 1; and

FIG. 4 is a fragmentary, enlarged sectional view of a joint betweencontainer sections.

ON THE DRAWING The reference numeral 10 indicates generally a suitablecontainer, or tank of highly dielectric structural material and ofcircular cross section. The container is preferably elongated andpositioned with its longer dimension horizontal. Said container 10, asshown, has a cylindrical wall 11 comprising a plurality of jointedsections 11a, 11b, and 11c, and vertical end walls 12 and 13. Anelectrode 14, serving as the cathode, suitably supported at a sectionjoint 15, extends transversely of the tank in spaced relation to the endwall 12 to provide a compartment 19 for the collection of deionizedwater passing through the cathode, 14 toward an outlet 20 positioned inthe end wall 12. A second electrode 18, serving as the anode, is mountedtransversely of the tank at a section joint 16 in spaced relation to theend wall 13 to provide a compartment 21 for deionized water. The endwall 13 is provided with an outlet 22 for lateral flow thereof from thecompartment 21. The outlets 20 and 22 are controlled by valves 23 and24, respectively, to regulate the effluent from the compartments 19 and21.

Feed water is introduced into the space S between the cathode 14 andanode 18 through a feed line 25 controlled by a valve 26. From the spaceS the feed water flows in opposite directions laterally through thecathode 14 and the anode 18, to their respective outlets 20 and 22. Thetank 10 is also provided with an outlet 27 having a valve 28 for thewithdrawal of water and any collection of settled solids from the spaceS at a controlled rate or at intermittent periods.

The cathode l4 and the anode 18 are each connected externally, as bywires 29 and 30, to a suitable source of unidirectional electriccurrent, such as DC electricity, (not shown). The cathode 14 is formedof any suitable ferrous metal, such as stainless steel, while the anodeI8 is formed of an inert material, such as platinum or other heavy metalor alloy, carbon, graphite, or the like. A voltage differential from aminimum of about 5.0, and preferably not less than about 10 volts, butnot over a maximum of about I00 volts, and preferably not over 50 voltsis established between the cathode 14 and the anode 18. Since the feedwater introduced through the valve controlled inlet 25 is practicallynonconductive of electricity, a sufficient voltage differential must beestablished to provide a current of about I to 20 milliamperes persquare centimeter, the current density selected being such as to cause adeionization of the water in its flow laterally through the cathode l4and anode 18 from the space S.

As best shown in FIGS. 3 and 4, each section joint, such as at 15, isformed by an interfitting tongue and groove construction of the opposedends of the sections 11a and 11b, but with an annular inner space 30therebetween for the reception of the electrode, in this case thecathode 14. The electrode 14 suitably comprises a metal wire ring 31 anda porous or foraminous disk 32, the periphery of which is partiallywrapped around said ring 31. The annular space 30 is of such dimensionsas to receive snugly the wrapped ring 31 and hold the ring andassociated disk 32 securely in place.

The cathode 14 can be formed of a foraminous or perforate disk of aferrous metal, such as a stainless steel screen, or other porous fabric,as indicated at 32a. The ends of wire ring 31 are carried out through ahole 33 (FIG. 3) to provide the connecting wires 29 to the source ofunidirectional current. A band 34 of flexible electricians tape is woundaround the container at the joint 15 to seal the joint.

Similarly, the anode 18 comprises a porous disk of fabric 35 supportedby a ring 36 and secured in an annular inner space 37. The anode,however, is formed of material that is inert to and not attacked by anyelectrolytic action set up in the operation of my system. For thispurpose, the anode can be of platinum, or of carbon or graphite, agraphite fabric or a graphitized glass fiber fabric being suitable. Thering 36 should also be of inert material with suitable strength, such asplatinum wire.

It will be understood, of course, that the apparatus illustrated anddescribed is of the laboratory type and that other forms of constructionfor commercial use can be readily devised.

DETAILED DESCRIPTION OF THE METHOD The source of water supplied as feedwater to my deionized system is, in general, a natural water containinga dissolved solids content of from 50 to 2,000 p.p.m. hardnesscalculated as CaCO with only negligible quantities of non-hardnessforming salts, such as sodium chloride. Accordingly, the feed water issubstantially nonconductive because of the substantial absence of highlyionized salts and only becomes conductive when a sufficiently highvoltage is impressed upon the electrolytic system that includes thecathode l4 and the anode 18.

The following examples will serve to illustrate the method of myinvention. These examples are given by way of illustration only and notby way of limitation:

EXAMPLE NO. I

In this example both electrodes were formed of graphite cloth to avoidintroducing any metal ions into the electrolytic system. Data wereobtained as to the deionization at the cathode or anode where the feedwater initially had the following analysis:

P-P- Two runs were made on successive days on the same feed Caco waterabove mentioned, and after the indicated number of Magnesium, calculatedas CaCO 290 Chlorine calculated as Nam 68 hours analyses were made ofthe cathode and anode efiluents, Sulfate. calculated as Na,so. s thevoltage being maintained at about 42 volts and the current After runs Aand B series of about 8 hours on successive 5 density within the rangeoffrom 2 to 5 ma. cm

Time, minutes:

days under the conditions indicated below, the analysis of the ln RunLN-3l no analysis was made of the effluents for final cathode effluentwas as shown: anions. Accordingly, a furtherrun L N-31A, was made, usingCurrent density Cathode Efliluent Analysis milliamps/ Run Volts sq. cm.Ca(CaCO3) Mg(CaCO Cl(NaCl) SO4(NazSO4) A1 42 4.4 8 37 12 33 B1 42 4. 4 463 (i) 13 A2 18 1. 5 9 8 (1) 3G B-2. 18 1. 6 6 90 5 57 1 Trace.

The final anode effluent corresponding to the above A and feed water ofan analysis similar to that in LN-30 and LN-3 l B series gave thefollowing analysis: asi aqisiyiqr JQPQWLQBQP @5993 Current density AnodeEflluent Analysis mtlliamps/ Run Volts sq. em. Ca(CO3) Mg(CaC 0.1)Cl(NaCl) SO4(N82SO4) A-l. 42 4. 4 80 77 104 773 B-l 42 4. 4 55 104 773A-Z. 18 l 5 69 109 132 1, 000 B2 18 1 6 72 92 105 956 t .H M

As shown by the foregoing data, the deionizing effect is which twosamples were taken, with the following results 7 most pronounced in thecathode effluent, where a decrease in hardness (total Ca and Mgcalculated as CaCO of from 555 in the feed water to a minimum of 17(A-2) and a maximum 525 2 58: bi e? Nggbf of 96 (B-Z) was found in thecathode effluent. D p- D-D- D-D- D-D- i T- I h 1 h 2 s 2 n t is examp e,t e e ectro ytic system was that s own 8 0 68 11811 I schematically inthe drawing, except that both electrodes Anode emuem 31 24 180 638comprised 50 mesh (US. Standard) stainless steel Screens NorE.-Thecurrent density was maintained at 10 maJcmfl.

potential of about 42 volts DC was applied across the electrodes.

I claim as my invention:

initially there was no detectable current flow through the 1. The methodof substantially deionizing water containing feed water in space S. Thefeed water was hard water containdissolved relatively insoluble,hardness-forming salts, which ing 325 ppm. Ca as CaCO and 289 ppm. Mg asCaCO;,, or a consists essentially of total of 614 ppm. of equivalentCaCO establishing a confined horizontally disposed flow path,

Conductivity was established in about one-half hour and the positioninga pair of spaced water-porous electrodes verticurrent increased slowly.leveling oil" at about 1.5 to 4.4 milcally arranged for immersion insaid flow path to provide liamperes tmu.) per square centimeter.Corrosion occurred at an inner compartment therebetween and compartmentsthe anode as shown by the formation offerrighydro ide.

Hm W

flowing feed water into said inner compartment for free 2. A method asdefined by claim 1, wherein said electrodes flow outwardly thereofthrough said respective porous are foraminous fabrics freely permeableto the flow of water electrodes into said outer compartments,therethrough.

passing a unidirectional electric current between said elec- 3. A methodas defined by claim 2, wherein solids settling trodes through the waterin said inner compartment out in said inner compartment are withdrawntherefrom. under a difi'erential voltage of at least 5 volts and notover 4. A method as defined by claim 1, wherein the current denabout 100volts for a sufficient length of time to effect a sity is maintained atabout 1 to milliamperes per square w substanfi deitmjgation ofsaidwatengnL icentimeter and the voltage is maintained at about l0-50 voltscollecting said substantially deionized water in said out- {for a periodof time of at least about 8 hours.

wardly arranged compartments. 10 1 a

2. A method as defined by claim 1, wherein said electrodes areforaminous fabrics freely permeable to the flow of water therethrough.3. A method as defined by claim 2, wherein solids settling out in saidinner compartment are withdrawn therefrom.
 4. A method as defined byclaim 1, wherein the current density is maintained at about 1 to 10milliamperes per square centimeter and the voltage is maintained atabout 10-50 volts for a period of time of at least about 8 hours.